Polythiophenes have been studied extensively due to their interesting electrical and/or optical properties. Polythiophenes become electrically conducting upon chemical or electrochemical oxidation or reduction.
EP-A 339 340 discloses a polythiophene containing structural units of the formula:
in which A denotes an optionally substituted C1-4-alkylene radical and its preparation by oxidative polymerization of the corresponding thiophene.
EP-A 440 957 discloses dispersions of polythiophenes, constructed from structural units of formula (I):
in which R1 and R2 independently of one another represent hydrogen or a C1-4-alkyl group or together form an optionally substituted C1-4-alkylene residue, in the presence of polyanions.
EP-A 686 662 discloses mixtures of A) neutral polythiophenes with the repeating structural unit of formula (I),
in which R1 and R2 independently of one another represent hydrogen or a C1–C4 alkyl group or together represent an optionally substituted C1–C4 alkylene residue, preferably an optionally with alkyl group substituted methylene, an optionally with C1–C12-alkyl or phenyl group substituted 1,2-ethylene residue or a 1,2-cyclohexene residue, and B) a di- or polyhydroxy- and/or carboxy groups or amide or lactam group containing organic compound; and conductive coatings therefrom which are tempered to increase their resistance preferably to <300 ohm/square. Examples of di- and polyhydroxy organic compounds disclosed in EP-A 686 662 are: sugar and sugar derivatives, such as saccharose, glucose, fructose, lactose, sugar alcohols, such as sorbitol and mannitol, and alcohols such as ethylene glycol, glycerine, diethylene glycol and triethylene glycol.
EP-A 1 122 274 discloses a process for preparing water-soluble π-conjugated polymers, characterized in that the monomer thiophene derivative according to formula (I)
in which X and Y are independently O, S, N—R1, Z is —(CH2)m—CR2R3—(CH2)n—; R1 is aryl, C1-18-alkyl or hydrogen; R2 is hydrogen or —(CH2)s—O—(CH2)p—SO3−M+; R3is —(CH2)s—O—(CH2)p—SO3−M+; M+ is a cation; m and n are independently a whole number from 0 to 3; s is a whole number from 0 to 10; and p is a whole number from 1 to 18; is polymerized by an oxidation agent in aqueous solution.
WO 01/78464 discloses in an organic/polymer electroluminescent (EL) device which comprises: a transparent substrate; a semitransparent electrode deposited on the transparent substrate; a hole-injecting layer positioned on the semitransparent electrode; an emissive layer made of an organic EL-material, positioned on the hole-injecting layer; and electron-injecting layer positioned on the electron-injecting layer, the improvement comprising that single-ion conductors are employed for the hole-injecting layer and the electron-injecting layer. The specification does not define the meaning of the term “single-ion conductor”, which in plain language means a conductor of a single ion, although claim 9 teaches that the single ion conductor can be a single-cation conductor or a single anion conductor and claim 10 teaches that such single ion conductors can be represented as a general formula (I) or (II), comprising ether chain [(—CH2)nO—] such as polyethylene oxide or polypropylene oxide in the main chain, and contains anions such as SO3−, COO− or I− in the main side chains that form ionic bonds with counter ions such as Na+, Li+, Zn2+, Mg2+, Eu3+, or (NH3)4+:
wherein, EO represents ethylene oxide; Non-EO represents non-ethylene oxide; PO represents propylene oxide; Non-PO represents non-propylene oxide; A− represents anion; C+ represents cation; m+n=11 and n represents a real number more than 0 and less than 1.
T. -W. Lee and O. O. Park disclosed in 2001 in Advanced Materials, volume 13, pages 1274–1278, polymer light-emitting energy-well devices using single-ion conductors (SIC's) in which charge injection and its confinement simultaneously in EL devices is striven for by using both a single-cationic conductor (SCC) and a single-anionic conductor (SAC), which “greatly improve the charge injection due to accumulation of the mobile ions near the electrodes” with the aim of “confining well-electrons and holes leading to enhanced recombination rate of the pairs” in devices in which “the mobile ions to play a key role in improvement of charge injection are separately located near both electrodes in the structure of a sandwiched multi-layer device instead of blending with the emitting material so that the problem of phase separation of the emitting materials can be avoided”. They further disclose that ionic polyurethane possesses good mechanical properties and high ionic conductivity with a single-ion transport character and that SIC's are generally of two different types: one is a polymer blend of an ionomer and polyether which usually possesses poor mechanical properties and the other is the copolymer of an oligomeric ionomer with polyether. They also disclosed that incorporation of the SIC's with soft and hard blocks into the EL devices dramatically improves not only luminance but also the efficiency and that SCC's possess electron-injecting and hole-blocking properties and SAC's possess hole-injecting and electron-blocking properties.
T. -W. Lee et al. disclosed in 2001 in Journal of Applied Physics, volume 90, pages 2128–2134, a study of the effect of ion concentration, neutralization level and counterions in ionomers to obtain the optimal electroluminescent (EL) characteristics in polymer light-emitting diodes using poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylenevinylene] (MEH-PPV) for the emissive layer and sulphonated polystyrene (SPS) ionomers for the electron-injecting layer.
A general problem in electronic devices, particularly in light emitting diodes, is undesirable hole-electron recombination at the positive electrode thereby reducing the efficiency and lifetime of the device.
A general drawback of electroconductive layers containing poly(3,4-dialkoxythiophene) polymers in the presence of a polyanion is the rapid increase in their surface resistance upon exposure to visible and UV light.
Aspects of the Invention
It is therefore an aspect of the present invention to provide electroconductive layers containing poly(3,4-dialkoxythiophene) polymers in the presence of a polyanion which do not undergo a rapid increase in their surface resistance upon exposure to visible and ultraviolet light.
It is a further aspect of the present invention to provide a layer between a positive electrode and a material capable of hole transport capable of reducing hole-electron recombination at the positive electrode thereby increasing the efficiency and lifetime of electronic devices containing such layer configurations.
Further aspects and advantages of the invention will become apparent from the description hereinafter.